Ecosystem services by wetlands for polluted water treatment

Abstract

Various designs are discussed for ecosystem services in engineered wetlands for contaminated water treatment. Techniques such as Rhizo filtration, Constructed wetlands and Floating rafts are highlighted based on our experiments. Specifically, enhanced bioenergy production by domestic wastewater treatment in rhizo filtration by fast growing trees is discussed. In another set of experiments, designs and factors which can enhance the rate of pollutant removal from wastewater by floating wetlands are seen. In a study extending over three years fast growing short rotation trees, eucalyptus (Eucalyptus hybrid), poplar (Populus deltoides), salix (Salix alba) and melia (Melia azedarach) were irrigated with domestic wastewater with ground water as control. It was seen that the calorific value of woody biomass grown using ground water was of the order 17.4-15.6MJ/kg and this was increased by 6.7 to 16% on wastewater irrigation. Thus, besides a significant increase in the yield biomass (2-4 times) there is a concurrent increase in the calorific value of wood, resulting in higher energy output by wastewater irrigation. TGA and FTIR of the samples did not show significant difference between waste water and ground water irrigated biomass. In the floating wetland study Canna indica was taken on floating rafts and the phytoremediation efficiency of the units was examined. Further the floating raft units were integrated with a constructed wetland to form a hybrid system to enhance the overall efficiency in water treatment. Changes in waste water characteristics with contact time were examined. Reduction in BOD and COD of waste water significant in 2-5 days of contact and this varies with the maturity and density of plants and roots. There is a significant reduction in bacterial load in terms of E. coli counts in parallel with BOD. Rate of reduction of contaminants is near first order. The dissolved oxygen (DO) levels increase with time.Various designs are discussed for ecosystem services in engineered wetlands for contaminated water treatment. Techniques such as Rhizo filtration, Constructed wetlands and Floating rafts are highlighted based on our experiments. Specifically, enhanced bioenergy production by domestic wastewater treatment in rhizo filtration by fast growing trees is discussed. In another set of experiments, designs and factors which can enhance the rate of pollutant removal from wastewater by floating wetlands are seen. In a study extending over three years fast growing short rotation trees, eucalyptus (Eucalyptus hybrid), poplar (Populus deltoides), salix (Salix alba) and melia (Melia azedarach) were irrigated with domestic wastewater with ground water as control. It was seen that the calorific value of woody biomass grown using ground water was of the order 17.4-15.6MJ/kg and this was increased by 6.7 to 16% on wastewater irrigation. Thus, besides a significant increase in the yield biomass (2-4 times) there is a concurr...